PF Correction Techniques in highly varying loadAtul Tare03.09.10

Contents

§ Issues faced in Industries§ Impact of varying loads on PF - various applications§ Impact of method of capacitor switching on Harmonics§ Impact of varying loads on DG sets§ Regulatory Initiatives§ Criteria for appropriate PF Improvement mechanism§ Solution you need

Issues Faced in Industries

§ Modernization of Industries – Shift to Electronic Controls§ Almost all loads (which were hitherto linear) became non

linear§ To maximize PF incentives, source side PF improvement

is attempted through Fixed capacitors or through APFC or slow response Thyristorized systems.

Issues Faced in Industries

§ While this helps maximize PF Incentive, PF under low load, fast changing loads, unbalanced loads is found either low lagging or leading.§ Improper method of capacitor switching is seen to

generate Harmonics.§ Unbalanced loading conditions are prevailing in the

industry.

Issues Faced in Industries

§ Equally distributed single phase loads across three phases are not necessarily a balanced load. § When one single phase load trips, the load becomes

unbalanced, calling for Unbalanced PF compensation.

Impact of varying loads on PF - various applications

Aluminum Rolling Mill application

Drive application

Furnace application

Mining application

CT Scan application

Unbalanced PF across phases

Impact of varying load on PF

Impact of varying load on PF

Resulting PF dropping to 0.01 lag momentarily

kVAr does not change adequately

When load changes

The load is changing ultra fast and is unbalanced across phases.

For the same load levels, the PF profile of individual phases remain unchanged ( with and without APFC) though the load is unbalanced. Average PF is leading with APFC

APFC not solution to all loads

Other Applications

§ High Rise Buildings where many lifts can operate at a time.§ Furnace Loads§ Industries where Heavy Motors are switched on

simultaneously§ Industries experiencing Voltage Flickering Problem.

Effect of Capacitor switching method on harmonics

Without capacitor

Withcapacitor

Impact of wrong compensation on harmonics

With every step of APFC, PF improves and THD I increases.% THD I increased from 13.8% to 22% on application of 200 kVAR Balanced APFC.

APFC Switched on

step 1step 2

step 3step 4

13.8% THD I

18.2% THD I

19.7% THD I

22.00% THD I

14.8% THD I

Impact of wrong compensation on harmonics

APFC Switched on

step 1 step 2 step 3 step 4

6.11% THD V

5.12% THD V

6.24% THD V

6.28% THD V5.55%

THD V

With every step of APFC, PF improves and THD V also increases. % THD V increased from 5.12% to 6.28 % on application of 200 kVAR Balanced APFC.

Effects of Harmonics

§ High harmonics results in:- Cable overheating in undersized cables- Cable line loss in oversized cables- Nuisance tripping of Breakers- Resonance blow up of Capacitors.- Damage to Power Transformer- Malfunctioning of Electronic Controls and devices

SOURCE AND LOAD SHOULD WORK IN HARMONY….

Load

LoadEB/DG

EB/DG

….POWER QUALITY ASSESSMENT AND CORRECTION ENSURES THIS OBJECTIVE.

Impacts of varying load on DG sets

§ DG Sets are the most vulnerable to varying loads:- Oversized or undersized DG resulting in high fuel

consumption or DG not taking load. - Production loss when DG not taking load- Increased inventory to cope up with power cuts- Poor Quality of products especially welding

components - increased rejection- Poor Power Factor

Regulatory Initiatives

§ Encourage customers to maintain a flat load profile.§ Bill customers on kVAHr instead of kWHr. PF

incentive is withdrawn.§ Consumers above 500 kVA contract demand will

have to declare Harmonic Levels and their plans to mitigate them. (Position varies from State to State).

Criteria - Appropriate PF Improvement solution

§ Rate of Change of Load§ Capacitor Switching Technique§ Type of load – Balanced or Unbalanced§ Source Independency§ DG Compatibility§ Harmonic Mitigation

What do you need?

§ The Solution should provide

- Cycle to Cycle Compensation In 20 milliseconds- Transient free switching- Curtailing harmonics to desired levels- Compatible to run on both DG and EB supply- Maintain Unity Power Factor under Unbalanced loading conditions

Cummins can help you with a System having features§ Cycle-by-cycle reactive power compensation

providing mirror image compensation§ Transient-Free Solid-state Capacitors Switching§ Energy Savings§ Compatible to both EB and DG§ Enhancement of generation capacity (DG Sets)§ Harmonic Filtration§ Prevention of Voltage drops, Reduction of Voltage

Flickering§ Comprehensive Power Quality Analyzer§ Self testing and comprehensive reporting feature

Thank You

Contact Us:

Atul TarePower ElectronicsCummins India LtdMob: 098505 63569Email: atul.tare@cummins.com